1. Field of the Invention
The present invention relates to sizing and biasing of devices utilized to form a circuit that satisfies a set of performance parameters.
2. Description of Related Art
Heretofore, custom integrated circuits were designed by interconnecting a plurality of devices such as transistors, resistors, capacitors, inductors, diodes, and the like to form cells. In a simple custom integrated circuit, one cell could form the entire circuit. However, in more complex circuits, an interconnection of plural cells may be needed to form the circuit.
Currently, two processes are utilized to design custom integrated circuits; namely, a bottom-up approach and a top-down approach. The bottom-up approach begins with cells in the lowest part of the design. After those cells are designed and connected together, the next level of cells are designed and connected together. This process continues until the circuit is complete.
At each level, the circuit's performance characteristic is measured and a decision is made whether further design is required at the current level, to begin design on the next level or to return to a lower level and redesign it. Redesign is typical because it is not easy to predict the performance of a design before detailed simulation, and detailed simulation requires that a design be well defined.
The top-down approach begins at the highest level in the circuit and derives the performance characteristic for each cell at that level. The design proceeds down each level until the cells at the lowest level have been defined in terms of devices. Like the bottom-up approach, redesign is typical and the design process is highly iterative. The main problems occur because accurately predicting the performance of cells before they are designed is difficult and error prone.
It is, therefore, an object of the present invention to overcome the above problems and others by providing a method of selecting cells utilized to form a circuit in a manner that avoids iterative redesign of one or more of the cells to achieve a circuit having a desired performance characteristic. Still other objects will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.